Under searchlight beams probing the night sky over Cairo, the crowd of thousands roared as one: "Inshallah" – God willing – "Mohamed Morsi will be president of Egypt." Excitement surged as flags waved, fireworks exploded and the country's most powerful political force exuded boisterous confidence that its hour had come.

"Just two days left," shouted the man on the podium, as speaker after speaker – from football stars to a stern-looking preacher – endorsed the candidate of Egypt's Justice and Development party, the political arm of the Muslim Brotherhood. "Keep up the hard work, and we will see victory in the first round."

Part election rally, part prayer meeting and part show of political strength, this was the final event before campaigning ended in advance of Wednesday's vote, when Egyptians will for the first time choose a leader without knowing the outcome in advance. And the race, say pundits and pollsters, is wide open.

Held half a mile from the cradle of the revolution in Tahrir Square, Sunday's FJP rally was a model of good-natured decorum. Male stewards were in T-shirts, beards optional but short; their women colleagues all wore the hijab. Separate seating was available for men and women, but segregation was not enforced.

Many came with their families. Asma Mohammed, a precocious 11-year-old, liked Morsi because he would implement the "Sharia of God, bring stability and solve unemployment". It was a rally of the converted. No one came to make up their mind. The national anthem underlined how rooted in Egyptian life this movement is.

The Cairo rally was replicated in all the country's 24 other governorates - evidence of the legendary powers of organisation and mobilisation the Brotherhood hopes will get the vote out for Morsi this week and in an almost certain runoff in mid-June.

Yet the candidate himself is uninspiring, a poor stand-in for the charismatic but disqualified Khairat al-Shater, a wealthy businessman and senior Brother. Egyptian journalists shook their heads in despair as Morsi finally spoke – only to utter a catalogue of unquotable platitudes. The hope is that ideology and discipline will win out over personality. "Morsi has a long history of political activity in opposition under the previous regime," said Muhammad Sa'ad, an engineer.

"In football can't a substitute come on with 10 minutes to go and score the winning goal?" asked Sheikh Mohammed Abdel-Maqsud.

Hesitant at the start of the revolution, the Brotherhood cleaned up in the parliamentary elections with 47% of the seats but has since suffered from a lacklustre performance by MPs, in part because the people's assembly's powers have been limited by the generals of the Supreme Council of the Armed Forces who are due to hand over power at the end of June.Suspicions of the Brotherhood and its violent and undemocratic past run deep among secular and liberal Egyptians. So there was anger and alarm when it reversed its initial decision not to field a presidential candidate, as there was when it packed the assembly charged with writing Egypt's new constitution.

According to a recent Gallup poll, its popularity has fallen steeply – from 63% in February to 43% in April. But it would clearly be premature to write it off or dismiss Morsi as a no-hope underdog. "People have taken heart from this decline, but I am not so sure," said one veteran Cairo observer, pointing to the Brotherhood's formidable ability to maintain support and stay on message and on top.Overall these are confusing times in Egyptian politics. Many feel that the revolution that overthrew Hosni Mubarak in 18 days in February 2011 has stalled and that the much-vaunted "transition" from military to civilian rule is endless and chaotic. Lost in Transition, is how one thinktank aptly titled a recent report on Egypt.

It is a curiosity of this election that the two main camps are split internally. Amr Moussa, the former foreign minister and frontrunning secular candidate, faces a serious challenge from Ahmed Shafiq, Mubarak's last prime minister, who critics scorn as a "fuloul" (remnant) of the discredited old regime.

On the Islamist side, Morsi is competing against the Brotherhood renegade and now independent Abdel-Moneim Abul-Futouh, who has diverse appeal and is feared by the military as far less compromising than the old enemy they know so well. It means that Islamist-minded Egyptians face difficult choices that could split the vote and play into the hands of their secular opponents. "If there had not been a Brotherhood candidate I would have voted for Abul Futouh," said Sa'ad as another round of cheering went up from the crowd. "Morsi is a good man. He faced the oppression of the tyrant so he will not be a tyrant himself."Abu Amr, a jovial fiftysomething former government employee, used to support Sheikh Hafez Abu Ismail, the disqualified Salafi candidate. "I am going to choose between Morsi and Abul Foutouh," he revealed, "but I haven't made up my mind."

In polling earlier this week Morsi jumped into third place for the first time with 14.8%, outscoring Abul-Fotouh by a tiny 0.2%. Analysts say it is Morsi's emphasis on Islamic principles that has given that edge. But the previous week, Morsi polled only 9.4%, suggesting he is gaining 0.6% daily, according to the Ahram Centre.

But if Egypt does elect an Islamist president, it will be one of the biggest of the earthquakes to have accompanied the Arab spring. And if Morsi should win, it will resonate across the Arab world and far beyond. Mohamed Hassanein Heikal, doyen of Egyptian journalists since the days of Nasser, posed the question starkly and clearly. "If Dr Mohamed Morsi, candidate of the Muslim Brotherhood, wins the presidential elections, will the state – from the presidency to parliament to the cabinet - be under Islamist control? Is this acceptable and sustainable?"